Grease a 9x13 inch baking pan with butter, set the pan aside.
In a large saucepan, combine the mini marshmallows and butter over medium heat. Cook until all the marshmallows are melted, making sure to stir occasionally.
Stir the vanilla extract and food coloring into the marshmallows. Once all the marshmallows are green, add in the rice krispies and stir until the cereal is coated.
Pour the mixture into the prepared pan, spray your hands or spatula with nonstick spray and press the rice crispy into an even layer.
Place the chocolate and coconut oil into a medium heat-safe mixing bowl. Microwave for 30-second intervals until the chocolate is melted, making sure to stir after every 30 seconds. .
Pour the chocolate over the Rice Krispies and spread it in an even layer.
Sprinkle the hearts all over the top of the chocolate. Place the pan in the fridge and allow the chocolate to set up for 15 to 20 minutes. Cut into squares and enjoy.